/* p9_2.c : single byte read from DS1337
 *
 * This program uses single byte read to get the second counter
 * of the DS1337 RTC chip. The three least significant bits of
 * the second counter are used to turn on/off the tri-color LEDs
 * on the LaunchPad board.
 * P6.5 - SCL, P6.4 - SDA
 *
 * No error checking is done in I2C code.
 *
 * Tested with Keil 5.20 and MSP432 Device Family Pack V2.2.0
 * on XMS432P401R Rev C.
 */

#include <stdio.h>
#include "msp.h"

void delayMs(int n);
void I2C1_init(void);
int I2C1_Read(int slaveAddr, unsigned char memAddr, unsigned char* data);
    
#define SLAVE_ADDR 0x68     // 1101 000.    DS1337

int main(void) {
    unsigned char data;

    P2->DIR |= 7;   /* P2.2, P2.1 ,P2.0 set as output for tri-color LEDs */
    I2C1_init();

    for (;;) {
        I2C1_Read(SLAVE_ADDR, 0, &data);    /* read second counter */
        P2->OUT = data;                     /* write to LEDs */
        delayMs(237);                       /* delay arbitrary time */
    }
}

/* configure UCB1 as I2C */
void I2C1_init(void) {
    EUSCI_B1->CTLW0 |= 1;           /* disable UCB1 during config */
    EUSCI_B1->CTLW0 = 0x0F81;       /* 7-bit slave addr, master, I2C, synch mode, use SMCLK */
    EUSCI_B1->BRW = 30;             /* set clock prescaler 3MHz / 30 = 100kHz */
    P6->SEL0 |= 0x30;               /* P6.5, P6.4 for UCB1 */
    P6->SEL1 &= ~0x30;
    EUSCI_B1->CTLW0 &= ~1;          /* enable UCB1 after config */
}

/* Read a single byte at memAddr
 * read: S-(slaveAddr+w)-ACK-memAddr-ACK-R-(saddr+r)-ACK-data-NACK-P
 */
int I2C1_Read(int slaveAddr, unsigned char memAddr, unsigned char* data) {
    EUSCI_B1->I2CSA = slaveAddr;    /* setup slave address */
    EUSCI_B1->CTLW0 |= 0x0010;      /* enable transmitter */
    EUSCI_B1->CTLW0 |= 0x0002;      /* generate START and send slave address */
    while((EUSCI_B1->CTLW0 & 2));   /* wait until slave address is sent */
    EUSCI_B1->TXBUF = memAddr;      /* send memory address to slave */
    while(!(EUSCI_B1->IFG & 2));    /* wait till it's ready to transmit */
    EUSCI_B1->CTLW0 &= ~0x0010;     /* enable receiver */
    EUSCI_B1->CTLW0 |= 0x0002;      /* generate RESTART and send slave address */
    while(EUSCI_B1->CTLW0 & 2);     /* wait till restart is finished */
    EUSCI_B1->CTLW0 |= 0x0004;      /* setup to send STOP after the byte is received */
    while(!(EUSCI_B1->IFG & 1));    /* wait till data is received */
    *data = EUSCI_B1->RXBUF;        /* read the received data */
    while(EUSCI_B1->CTLW0 & 4) ;    /* wait until STOP is sent */
    return 0;                       /* no error */
}

/* system clock at 3 MHz */
void delayMs(int n) {
    int i, j;

    for (j = 0; j < n; j++)
        for (i = 750; i > 0; i--);      /* delay 1 ms */
}